This application proposes continuation of a highly successful interdisciplinary training program in infectious diseases research that is based on the tenet that both MD and PhD postdoctoral research trainees benefit enormously from exposure to faculty and trainees from both backgrounds. The program, whose research emphasis is on the interface between human host and microbial (bacterial and viral) pathogens, provides an intense mentored research experience for MD and PhD postdoctoral trainees in infectious diseases. This occurs in conjunction with an individualized curriculum of didactic courses, seminars and journal clubs designed to encourage substantive interactions between MDs and PhDs. A short- term 3-month research experience for medical students is also offered. Most faculty are drawn from 1 basic science and 2 clinical departments, as well as 2 interdisciplinary PhD programs. Collaboration among program faculty is high. Research facilities are superb. The scientific program centers around three major areas: 1) Host Defense, emphasizing innate immunity; 2) Bacterial Pathogenesis; and 3) Viral Pathogenesis. Faculty are divided into: 1) full members; and 2) associate members; on the basis of their extramural research support and their experience both as an independent investigator and research mentor. Primary research mentors come from faculty meeting the criteria for full membership. An important aspect of the 3-year research experience for MD postdoctoral trainees with minimal prior research experience is an intensive exposure to a broad spectrum of graduate level basic science courses. All postdoctoral trainees establish a Research Advisory Committee. All trainees attend a research conference, as well as a seminar/ journal club designed to encourage cross-fertilization of ideas and scientific approaches between clinical medicine and basic science. They will interact with outstanding visiting scientists, attend scientific meetings, learn scientific writing and grant preparation skills, and complete a course in research and biomedical ethics. A recruitment program for minority trainees is in place and is being further expanded. In summary, this proposal requests continuation of an ongoing training program with an excellent training record which will provide a coordinated and integrated training experience for postdoctoral MD and PhD trainees in infectious diseases research related to the microbial pathogenesis of bacterial and viral infections of humans